Entangled electrons pave way for future quantum networks

By Tereza Pultarova

Published Wednesday, July 1, 2015

Japanese researchers have created a pair of spin-entangled electrons that maintain their link even when separated on a chip.

The breakthrough demonstration could pave the way for futuristic quantum networks based on quantum teleportation. Such networks would be able to share information contained in quantum bits, or qubits, between many elements on a chip - a key requirement to scale up the power of a quantum computer.

The experiment, led by a team from Japan’s RIKEN Centre for Emergent Matter Science, was described in the latest issue of Nature Communications.

"We set out to demonstrate that spin-entangled electrons could be reliably produced,” said researcher Russell Deacon. “So far, researchers have been successful in creating entangled photons, since photons are extremely stable and do not interact.”

The possibility to create non-local entangled electron pairs was in theory described by Albert Einstein, Boris Podolsky and Nathan Rosen. However, researchers so far struggled to complete the experiment in practice.

“Electrons are profoundly affected by their environment,” said Deacon. “We chose to try to show that electrons can be entangled through their spin, a property that is relatively stable."

The team had to first create a miniature device only a few nanometres in size that would allow them to take two electrons and get them across a junction between two superconductor leads to pass through two separate quantum dots.

“If we could detect a superconducting current, this would mean that the electrons - which can be used as quantum bits - remain entangled even when they have been separated between the quantum dots,” Deacon explained.

“We confirm this separation by measuring a superconducting current that develops when they split and are recombined in the second lead.”

The quantum dots, each around 100 nanometers in size, were grown at random positions on a semiconductor chip.

“Since we have demonstrated that the electrons remain entangled even when separated, we could now use a similar, albeit more complex, device to prepare entangled electron pairs to teleport qubit states across a chip,” Deacon said.

Electron spin is a convenient property to use for such experiments as it is relatively free from the environment and lasts a reasonably long time, the researchers explained. On a system level, spin-entangled electrons could be used to create photons that themselves would be entangled. This way, the engineers could create large networks to share quantum information on a wider scale.